The longer the half-life of the drug, the longer it will take to reach a therapeutic level, i. While Tegretol carbamazepine has a variable half-life initial half-life values range from hours, decreasing to hours on repeated doses , it also causes auto-induction of metabolism, so an initially therapeutic blood level can drop and that is why serum levels need to be followed more frequently initially with this medication.
Your doctor will explain how long it will take for your medicine to work, but you must work with him or her to ensure that you take the medication at the recommended dosage at the right time. Because of the long half-life, maintaining therapeutic levels takes attention to detail and focus, something that may be hard to maintain for those with bipolar disorders. As you and your family members work through your diagnosis, be sure to keep track of your medications and have someone equally accountable for you so that you don't miss a dose and render your medication ineffective, or worse risk too much medication in your blood, which could be toxic.
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I Accept Show Purposes. Was this page helpful? Indirect evidence may be gained from identifying RCTs that have compared the drug against a common comparator likely placebo , and then analysing whether studies in which a higher serum concentration was achieved demonstrated better effects on beneficial and harmful outcomes.
Combinations of indexing terms such as Medical subject headings MeSH and textwords should be used by reviewers to form a search strategy that maximizes sensitivity whilst minimizing specificity whilst keeping the number of records to sift manageable within the logistical constraints of the review.
RCTs comparing drug to placebo. An assessment of quality allows the reviewers to present the degree to which the results in the available literature are likely to be valid and robust, and whether conclusions that impact on clinical practice should be implemented.
There are specific considerations when conducting a systematic review of therapeutic ranges. There are a large number of critical appraisal tools for different study designs, each with varying emphasis on different aspects of quality, although many lack information on how they were developed [ 33 ]. These tools were not devised for the appraisal of therapeutic drug monitoring studies specifically, and therefore they may not address specific concerns when assessing the quality of included studies in reviews investigating the optimum therapeutic range of a drug.
This tool was developed for systematic reviews investigating the efficacy of an intervention, and allows a systemic and consistent approach to all included RCTs.
Though this tool allows a systemic and consistent approach, it is limited by its inter-assessor variability, and its tendency to judge older studies as a higher risk of bias. Although a specific systematic assessment tool for TDM studies is yet to be developed, we suggest the following considerations to be integrated into the quality assessment of included studies. Different assays vary in accuracy and this can lead to misleading measurements of serum concentrations and reviewers should consider the appropriateness of the methods for determining serum drug concentrations in individual participants.
Furthermore, drug clearance is a dynamic process and the time period between drug administration and serum measurement should be consistent between participants.
Selected outcomes should adequately represent harm and benefit, and techniques for measuring adverse effects should be decided a priori as ad hoc measurement of adverse effects carries risk of selective outcome reporting which could misinform the upper limit of a therapeutic range.
Data synthesis in systematic reviews of therapeutic ranges will involve a comparison of outcomes between participants who demonstrate differing serum levels of a drug. Studies vary in how they summarize the serum levels, and this will impact the approach to meta-analysis.
For example, studies may compare mean serum levels between those responding to the drug and those not or experiencing an adverse event or not continuous data , in which case a meta-analysis of differences in means can be undertaken to provide a pooled estimate of the difference. Alternatively, studies may compare numbers responding and not responding to a drug or experiencing an adverse event or not between those with serum levels below and above a particular threshold dichotomous data.
In such studies it would be common to report the relative risk or odds ratio of the event of interest, in which case a meta-analysis of the effect estimates can be undertaken to provide a pooled effect estimate. In any case, it is important to assess for heterogeneity between studies, and utilising a random effects approach to meta-analysis is recommended where the heterogeneity is found to be large. Potential sources of heterogeneity can also be explored by subgroup analyses and, where possible, meta-regression.
It is important to note that conducting a meta-analysis may not always be possible within a systematic review, and should only be undertaken where there are a sufficient number of studies with comparable outcomes and exposure groups.
For example, where patients are grouped according to a drug level threshold, it may only be appropriate to meta-analyse studies which utilize the same, or at least similar, threshold, and some thought would need to be given as to what range of thresholds would be considered similar.
In reviews appraising the evidence around a standard therapeutic range used in practice, the results may have four possible implications. The range may be appropriate, the upper or lower limit should be amended in light of the review results, or there is no evidence on which to make any recommendations Table 4.
The quality of the evidence around the recommendations of the review should be presented, in context of a summary of the population, indication, and outcomes included in the review. Consistency in the searching, selection and appraisal of studies is necessary if these reviews are to inform prescribing practice.
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